Goldman-Shen Pulse Sequence Research Articles

Non-Conventional Time Domain (TD)-NMR Approaches for Food Quality: Case of Gelatin-Based Candies as a Model Food.

The TD-NMR technique mostly involves the use of T1 (spin-lattice) and T2 (spin-spin) relaxation times to explain the changes occurring in food systems. However, these relaxation times are affected by many factors and might not always be the best indicators to work with in food-related TD-NMR studies. In this study, the non-conventional TD-NMR approaches of Solid Echo (SE)/Magic Sandwich Echo (MSE) and Spin Diffusion in food systems were used for the first time. Soft confectionary gelatin gels were formulated and conventional (T1) and non-conventional (SE, MSE and Spin Diffusion) TD-NMR experiments were performed. Corn syrups with different glucose/fructose compositions were used to prepare the soft candies. Hardness, °Brix (°Bx), and water activity (aw) measurements were also conducted complementary to NMR experiments. Relaxation times changed (p < 0.05) with respect to syrup type with no obvious trend. SE/MSE experiments were performed to calculate the crystallinity of the samples. Samples prepared with fructose had the lowest crystallinity values (p < 0.05). Spin Diffusion experiments were performed by using Goldman–Shen pulse sequence and the interface thickness (d) was calculated. Interface thickness values showed a wide range of variation (p < 0.05). Results showed that non-conventional NMR approaches had high potential to be utilized in food systems for quality control purposes.

One- and Two-Dimensional NMR in Studying Wood–Water Interaction at Moisturizing Spruce. Anisotropy of Water Self-Diffusion

This paper examines how wetting the surface of wood affects characteristics of wood materials. An important question is how moisturizing wood has an effect on diffusion parameters of water, which will change conditions of the technological treatment of material. A fibrous structure of wood can result in different diffusivities of water in the perpendicular direction and along the wood fibers. The work explores how 1- and 2-dimensional NMR with pulsed field gradients (PFG) highlights an anisotropic diffusion of water when moisturizing spruce wood. The methods applied: T2-relaxation (CPMG) measurements with the application of inverse Laplace transform (ILT), cross-relaxation experiments (Goldman–Shen pulse sequence), 1D PFG NMR on oriented wood pieces or applying gradients in various orientation, and 2D diffusion-diffusion correlation spectroscopy (DDCOSY) with two pairs of colinear gradient pulses. The results showed anisotropic restricted diffusion correlating the size of tracheid cells. The experimental 2D diffusion-diffusion correlation maps were compared with model calculations based on parameters of 2D experiment on spruce and the theory of 2D DDCOSY with ILT. Moisturizing spruce wood resulted in anisotropic diffusion coefficient which can be monitored in 2D NMR to discover different diffusion coefficients of water along the axis of wood fibers and in orthogonal direction.

The hydration of paper studied with solid-state magnetisation-exchange 1H NMR spectroscopy

Abstract The wide-line 1H nuclear magnetic resonance (NMR) spectrum of paper in equilibrium with ambient humidity consists of super-imposed relatively broad and narrow lines. The narrower line is of the order of 2 kHz wide at half the maximum height, while the broader line is of the order of 40 kHz in width at half height. On the basis of these line widths, the narrow line is assigned to water sorbed to the paper, and the broad line to the polymeric constituents of the paper. It was not possible to distinguish between the various polymeric components of paper contributing to the 1H NMR spectra. A modified Goldman-Shen pulse sequence was used to generate a spatial magnetisation gradient between the polymer and water phases. The exchange of magnetisation between protons associated with water and those associated with the macromolecules in paper was observed. The exchange of magnetisation is discussed within a heat transfer model for homonuclear dipolar coupling, with exchange being characterised by a spin-diffusion coefficient. Consideration of the magnitude of the initial rate of the exchange process and estimates of the spin-spin relaxation times based on 1H line widths indicate that some water must exist in a sufficiently immobile state as to allow homonuclear dipolar interactions between adjacent polymer and water protons. Thus, water sorbed onto paper must exist in at least two states in mass exchange with each other. This observation allows certain conclusions to be drawn about the ratio of free/bound water as a function of moisture content and the dispersal of water within the polymer matrix.

Characterization of Micro-Domain Structure of Solvent-Swollen Coal by Proton Spin Diffusion and Small Angle Neutron Scattering

The macromolecular structure of a high volatile bituminous coal (the Blind Canyon) is characterized by osmotic dilation experiments using deuterated solvents (pyridine or benzene/pyridine mixed solvent). Nano scale structural changes were quantitatively revealed using proton spin diffusion experiments and qualitatively verified with small-angle neutron scattering (SANS) measurements. The SANS data reveal systematic changes in the coherent scattering behavior of osmotically dilated coal particles in a binary solvent system of benzene + pyridine. These results show that volumetric strain derived from osmotic stresses results in the development of phase-separated domains at nanoscales. Quantitatively, the effect of solvent-to-coal mass ratio (S/C) on the proton relaxation characteristics was examined. It is shown that the fractional amount of mobile hydrogen yielding the exponential decay, fMH, increased to a maximum of 0.5 with increasing solvent concentration. Above S/C = 2.24, fMH remained nearly constant, indicating that solvent impenetrable regions exist in the swollen coal even at S/C ratios as high as 4.72. Although there exist at least two distinct structural regions in the swollen coals based on the transverse relaxation characteristics, longitudinal relaxation experiments are fit best by a single component revealing that spin diffusion is rapid in the swollen coals. The dynamics of spin diffusion were determined using a partially modified Goldman-Shen pulse sequence and analyzed by simple geometric models of two-phase systems. The average distance between the adjacent solvent impenetrable domains, di, was estimated on the basis of the diffusive path length for each spatial dimension by employing simple one-, two-, and three-dimensional models. Estimates of di derived from the SANS data lie between those derived for the one- and two-dimensional diffusion models suggesting that the actual structure may be roughly laminar, but with sufficient curvature or other irregularity to yield diffusion behavior lying between the two simple models considered. The results of this study clearly reveal that volumetrically measured osmotic strain is not affine down to the macromolecular level.

Microheterogeneity of Solvent-Swollen Coal Probed by Proton Spin Diffusion

The phase-separated structure of solvent-swollen coal was characterized using its proton flip-flop spin diffusion property. Five coals of different ranks were swollen by saturation with deuterated pyridine and were subjected to 1 H NMR relaxation measurements. At least two distinct structural regions exist in the swollen coals based on the transverse relaxation characteristics as reported in the literature. The observed longitudinal relaxation was characterized by a single component, since spin diffusion, i.e., the transfer of 1 H magnetization from the mobile to the rigid phase is active in the swollen coals. The process of this transfer was monitored using a partially modified Goldman-Shen pulse sequence and analyzed with a simple model. It is shown that coal swells in a nonuniform fashion on a fine scale and that phase separation occurs on a scale ranging up to 20 nm even in good solvents such as pyridine.

Structural analysis of core-shell type polymer particles composed of poly(butyl acrylate) and poly(methyl methacrylate) by high-resolution solid-state [formula omitted] n.m.r. spectroscopy

The phase-separated structure and molecular mobility for core-shell type polymer particles composed of poly(butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) have been examined by high-resolution solid-state 13 C n.m.r. spectroscopy. These types of polymer particles were prepared by the two-step emulsion polymerization of BA and MMA in the presence or absence of ally methacrylate (AMA) as a crosslinking agent. The analysis of the 1 H – 13C cross polarization process has revealed that molecular mobility of the main-chain of PBA is significantly restricted for sample BA2M prepared in the presence of 1.6 wt% AMA. 1 H spin–lattice relaxation time measurements in the rotating frame have also revealed that the PBA and PMMA phases are phase-separated in a scale of several nm for the polymer particles. Furthermore, the 1 H spin diffusion process, measured by the combined pulse sequence of the Goldman–Shen pulse sequence and the CP process, has been successfully analyzed in terms of the equation derived by the simple two-spin cross relaxation theory. The time constant T SD for the 1 H spin diffusion between two polymers obtained through this analysis has been found to be a useful parameter to elucidate the phase-separated structure. On the basis of these results, it is concluded that the PBA/PMMA polymer particles have a rather incompletely phase-separated core-shell type structure but the addition of an appropriate amount of AMA improves such a structure by confining the distribution of PMMA domains around the surface of the polymer particles probably as a result of the preferential crosslinking in the PBA phase.

Computer Simulations of the Goldman-Shen Experiment: Evaluation of Techniques for Minimizing the Influence of Spin-Lattice Relaxation

The magnetization of the mobile domain for a lamellar two-region system following the application of the Goldman–Shen pulse sequence was simulated under various conditions in order to evaluate the effectiveness of several suggested techniques for obtaining spin diffusion data separate from the effects of spin–lattice relaxation. It is shown that in general none of the methods are completely effective, but the conditions of applicability are discussed and simulated examples showing deviations from ideality are illustrated. © 1997 by John Wiley & Sons, Ltd.

Studies of domain morphology in segmented polyurethanes by pulsed NMR

A new technique based on the Goldman-Shen pulse sequence with varying preparation interval is proposed for the study of domain morphology of segmented polyurethanes. The results of numerical calculations of the magnetization recovery in different models of domain morphology show that the method provides new information about the domain morphology which is beyond the reach of the conventional Goldman-Shen experiment. A close agreement of the theoretical predictions with the experimental data on samples of segmented polyurethanes with a fixed molecular mass of the hard blocks and variable molecular mass of the soft blocks reinforces the above statement. The resulting structural parameters obtained by this new NMR technique are compared with the data from the small-angle X-ray scattering (SAXS) method.

Dipole-Echo Formation in Three-Pulse-Sequence NMR Experiments on Polymer Systems

Data from three-pulse NMR experiments, namely, the Goldman–Shen pulse sequence and the stimulated-echo sequence, on partially crystallized poly(ethylene glycol) and tetrafunctional dimethylsiloxane networks are presented. A dipole echo has been observed after a third radiofrequency pulse. Quantum mechanical calculations of the response of the spin system to the three-pulse sequences have been performed, considering only thez–zcomponent of the dipole–dipole spin coupling. The resulting expression suggests dipole-echo formation and is in agreement with experimental data.

Reconsideration of the NMR three-pulse responses of methyl protons in CH3COONa.3D2O

The response of triads of strongly coupled spin-1/2 nuclei to the generalized Goldman-Shen pulse sequence ( alpha )phi - tau 1-( alpha )phi +180 degrees - tau 2-( beta )0 degrees is reconsidered by taking into account the spin diffusion between the equidistant energy-level pairs of the spin-rotor system during the time tau 2. The refined theory gives quantitatively correct model responses and sheds new light on the discrepancy between the previous theory for an ensemble of isolated triads and the analogous theory for pairs of coupled triads, in the limit of no coupling. Theoretical three-pulse spectra are compared with experimental responses of the tunnelling methyl protons in a CH3COONa.3D2O single crystal at 30 K.

Response of Pairs of Spin-[formula omitted] Triads to the Generalized Goldman-Shen Pulse Sequence

The responses of six dipolar-coupled spins-12, forming a pair of equivalent triads, to a single resonant RF pulse and to the generalized Goldman-Shen pulse sequence (α)φ—τ1—(α)φ+ 180°—τ2—(β)0° are studied. Analytical expressions relating the Fourier spectra of the responses to the energy-level populations and the pulse-sequence parameters, τ1, α, and β are found for two relatively weakly interacting triads which reorient rapidly in a high external magnetic field. The theoretical NMR spectra are compared with proton and fluorine spectra in single crystals of CF3COOAg, CH3COONa·3D2O, and CH3COOLi·2D2O, each of which contains pairs of CF3 or CH3 groups.

A high-resolution solid-state NMR study of the miscibility, morphology, and toughening mechanism of polystyrene with poly(2,6-dimethyl-1,4-phenylene oxide) blends

An extended Goldman-Shen pulse sequence was used to observe indirectly the proton spin diffusion in the blends of polystyrene (PS) with poly(2,6-dimethyl-1,4-phenylene oxides) (PPO). The results indicate that the average distance between PS and PPO is less than 5 angstrom in the intimately mixed phase, but there are heterogeneous domains on a 100-angstrom scale. The data of spin relaxation of carbons, T1(C), for homopolymers and their blends suggest that there is a strong pi-pi electron conjugation interaction between the aromatic rings of PS and those of PPO, while the aromatic rings of PPO drive the aromatic rings of PS to move cooperatively. It is the cooperative motion that markedly improves the impact strength of PS.

Pulsed NMR Study of Motional Heterogeneity in Acrylonitrile-Butadiene/Poly(Vinyl Chloride) Blends

Abstract Motional heterogeneity in blends of NBR (AN = 38%) and PVC was studied by 1H pulsed NMR. It was estimated from NMR relaxation measurements that the PVC molecules in the NBR phase form phase domains of the order of less than 10 nm, consistent with the microheterogeneous structure observed by TEM. Furthermore, by spin diffusion experiments using the Goldman-Shen pulse sequence, the size of the PVC phase domains was semiquantitatively evaluated to be 4.2 nm in the case of the cylindrical domains and to be 5.1 nm in the case of the spherical domains. It becomes clear that pulsed NMR complements the results of other analytical methods with more detailed information on the state of the molecular mixing in the blends.

Proton spin diffusion monitored by 13C NMR

Proton spin diffusion can be monitored by combining a modified Goldman—Shen pulse sequence with cross polarization to 13C nuclei. A new procedure for presenting the results suppresses sensitivity to proton spin—lattice relaxation processes. Domain dimensions can then be estimated from published analytical expressions derived for spin diffusion in the absence of spin-lattice relaxation.

A modified Goldman-Shen NMR pulse sequence

A method for eliminating the T 1 effect during the spin diffusion process in the laboratory frame is presented using a modified Goldman-Shen pulse sequence.